72 454 auto TCS system questions

[Randall K.]

While reassembling my drive-side cluster and associated wiring, I noticed that there is no relay in the TCS relay connector.

What does TCS do?

Did my car use TCS?

If so, what is the effect of this relay not being populated in the harness?

Thanks
Randy

[Edward J.]

Re: 72 454 auto TCS system questions

[QUOTE=Randall Krohn (43621);600493]While reassembling my drive-side cluster and associated wiring, I noticed that there is no relay in the TCS relay connector.

What does TCS do?

Did my car use TCS?

If so, what is the effect of this relay not being populated in the harness?


The TCS system has a couple of features, cold start vacuum advance operation and if the car temp starts to get about 236 it will activate the vacuum advance system. also on the automatic cars when transmisson is in reverse its activated with the 20 sec. delay. I maybe missing something but if you have shop manuel it explains the full operation.

Randell, the relay you are looking for is behind the console instrument panel and is a delay relay for the TCS system on the big block

Your car should have a TCS system.

If the system is missing, which alot cars in those days they were unhooked or just done away with. If your planning on having the car judged, It will be tested during the operation check during flite judging.

[Joe L.]

Re: 72 454 auto TCS system questions

While reassembling my drive-side cluster and associated wiring, I noticed that there is no relay in the TCS relay connector.

What does TCS do?

Did my car use TCS?

If so, what is the effect of this relay not being populated in the harness?

Thanks
Randy

Randy-----


TCS is an abbreviation for "Transmission Controlled Spark". This was an emissions control system used to disable the distributor vacuum advance when the transmission was in certain gears. It has a power-robbing and reduced fuel economy "side effect". Many folks disabled the TCS system as a result. Both manual and auto trans-equipped cars received the TCS system. Your car did originally use TCS and the effect of the relay not being in place is that the system will be effectively disabled but it may be disabled in a way that the distributor vacuum advance does not work in all gears. The best way to disable the system is to bypass the TCS solenoid (on the manifold or carb) and route vacuum directly to the distributor vacuum control.

However, if you're having the car judged, you need to have the TCS system completely intact and operational to receive full points.

[Randall K.]

Re: 72 454 auto TCS system questions

Thanks, Joe and Ed, for the education. Shopping now for relay and TCS jumper harness (which was completely destroyed), and will engineer a reversible way to disable TCS at the solenoid.

Randy

[Jim T.]

Re: 72 454 auto TCS system questions

Randall I first learned about the TCS right after I bought a new 1970 Corvette 350/300 with turbo automatic. Bought it in August 1970 and bypassed the TCS in September 1970 and it is still that way today. Full time vacuum from a full time vacuum source on the carb to the distributor vacuum advance will increase gas mileage in city driving. It will also contribute to controlling engine temperature in city stop and go traffic in hot weather.

[Joe L.]

Re: 72 454 auto TCS system questions

Thanks, Joe and Ed, for the education. Shopping now for relay and TCS jumper harness (which was completely destroyed), and will engineer a reversible way to disable TCS at the solenoid.

Randy

Randy-----


The underdash relay is the TCS DELAY relay. It was GM #3996297. It's been discontinued for quite some time but finding one, even NOS, is quite easy. Why? Well, this is not the kind of part that most folks ever replace. In fact, quite the contrary. They are removed and junked while they are still serviceable or simply "abandoned in place". You can pick these up quite easily. There are several for sale on eBay right now.

As far as the harness goes, that's a different story. You will have to see if a source like Lectric Limited or M&H Electrical Fabricators will sell you this component of the harness. I doubt they will. Otherwise, you'll need to find a good used harness and remove the section you need and splice it in.

[Bill C.]

Re: 72 454 auto TCS system questions

I am 99% sure that the 1972 454 cars did not have a relay plugged in.
there was a jumper there only.

The 350 cars only had that relay.

[Randall K.]

Re: 72 454 auto TCS system questions

Hmmm... I'm not getting less confused here...

The Chevrolet Service Manual isn't definitive. Page 6T-17 describes 3 different TCS systems for Mark IV engines. The conclusion I'm lead to at this point is that Corvettes with RPO U14 (gauge package) only used the low-temperature 2-terminal switch on the right side of the block (matching what is now in my engine). Figure 6T-37 on the same page does not show the time-delay TCS relay...

I don't have a PV guide, so I don't know how this might be checked during judging.

Any more opinions out there??

Thanks
Randy

[Randall K.]

Re: 72 454 auto TCS system questions

Oops - forgot that I actually did have a PV guide. Text says "there will be a 20 to 30 second delay with 350 CID engines in 1972". I assume this means that big blocks have no delay - therefore no TCS delay relay...

Everyone agree??

Thanks
Randy

[Terry M.]

Re: 72 454 auto TCS system questions

I remember a page in the AIM for LS5 that says to install a jumper for LS5. I believe that was the 1972 AIM, but I get requests to look at a lot of the 1968-72 AIMS and I can easily lose track.

[Randall K.]

Re: 72 454 auto TCS system questions

Terry - that was the clue I needed. Damn, it's hard to find stuff sometimes in the AIM!

Anyhow, for non-BB engines, AIM UPC 12 sheet B5 shows the TCS relay and connector.

AIM UPC LS5 sheet A10 shows the jumper you referred to. I saw this previously, but "TCS" appears nowhere on this sheet! So, now to find a jumper or just make something...

Thanks!!!
Randy

[Alan S.]

Re: 72 454 auto TCS system questions

Hi Randall,
Member Jack Humphrey wrote an informative article about the 71 CEC system that appeared in the RESTORER, Vol. 35, Spring 2009.
Although the 70 and 72 TCS systems were a bit different, he makes some interesting comments about their operation too.
You might want to check it out if you decide to get your system operating properly.
Regards,
Alan

[Terry M.]

Re: 72 454 auto TCS system questions

I would bet that "jumper" was not too sophisticated -- and where it is at no one will ever see it. Just be sure it is solid. You don't want to have to get back in there.

[Bill C.]

Re: 72 454 auto TCS system questions

the jumper kind of looks like a new style fuse with the two blades and a cross over.
Mine was taped around the harness to keep it in.